A histological study of tissues and organs of rats deprived of leucine for a period of 30 days showed that the histological alterations were non-specific and similar to the effects of protein deficiency and/or nonspecific effects of other deficiencies. Normal, pair-fed and paired-weight control groups were included in this pilot study. In a study of the gastric mucosa of rats fed DDT in corn oil by intubation, electron microscopic examination of gastric fundic glands revealed that some parietal cells were significantly altered as compared with normal parietal cells. The altered cells were determined to be parietal cells on the basis that intracellular canaliculi were definitely present. Numerous prominent, large, polymorphic, dense, membrane-bounded bodies (or granules), which were interpreted to be lysosomes, were present. The agranular endoplasmic reticulum was reduced in quantity, while a significant increase in rough endoplasmic reticulum was noted. While the mitochondria were fewer than normal for parietal cells, these organelles were much larger than normal. Bundles of microfilaments and microtubules were sometimes very prominent.